Method for purifying TiO2 ore

ABSTRACT

Process for purifying TiO 2  ore consisting essentially of subjecting the ore to two or more leaching treatments, said leaching treatments alternating between use of an aqueous solution of a mineral acid and an aqueous solution of an alkali metal compound selected from the group consisting essentially of alkali metal carbonates, hydroxides or mixtures thereof.

BACKGROUND OF THE INVENTION

This invention relates to an improved method for purifying TiO₂ orewhich contains numerous impurities. The purified ore can be used to makeTiO₂

pigment or titanium metal or be used in any other process where apurified TiO₂ ore is required.

Currently, approximately 75 percent of the titanium minerals produced inthe world are utilized by the pigments industry to produce TiO₂ In theproduction of TiO₂ by the chloride process, beneficiated ore is usedwhich generally contains about 55-96% TiO₂. However, known beneficiationprocesses do not appear to be capable of satisfactorily purifying TiO₂ore which contains numerous impurities such as alkali metals, alkalineearth metals, rare earth metals, iron, aluminum, phosphorus, thorium,uranium, chromium, manganese, silicon, vanadium, and yttrium. Theseimpurities may be present as oxides, salts, or other complex forms andgenerally cannot be readily removed by conventional mechanical means oreven conventional chemical means. Especially detrimental to the chlorideprocess are such ores which contain in considerable quantity theimpurities of iron, calcium, silicon, aluminum, phosphorus, magnesium,barium and strontium, and radionuclides such as thorium and uranium. Forexample, phosphorus can cause processing problems in the TiO₂ process,and thorium and uranium may concentrate in the TiO₂ process and presenta potential health hazard. Also, the impurities of aluminum, phosphorus,silicon, thorium, and uranium are additionally a problem because theyare especially resistant to removal by conventional mechanical orchemical means.

Being able to remove such impurities efficiently would be highlydesirable because known sources of TiO₂ ore not containing suchimpurities are becoming increasingly scarce and expensive. Conversely,there exist large bodies of inexpensive carbonatite anatase ores whichare rich in TiO₂ but also contain significant quantities of suchimpurities. Moreover, while other processes to purify TiO₂ ore areknown, it appears that they either require additional, more complex ormore expensive processing steps or are deficient in one or more benefitsas compared to the process of this invention.

The following information is disclosed which may be of interest to thisinvention:

U.S. Pat. No. 4,176,159 discloses a process for the removal ofimpurities from titanium minerals. The process requires high temperaturecalcining, cooling, reducing, cooling, magnetic separation, mineral acidleaching, neutralizing, and washing.

U.S. Pat. No. 4,038,363 discloses upgrading of titanium values in a slagsuch as Sorels slag by roasting with an alkali salt, leaching withsulfuric acid in two stages, and calcining.

Japanese patent 48,102,712 discloses dephosphorization of titaniumconcentrates using caustic alkali after prior removal of iron.

Japanese patent 87-33058/47 discloses production of rutile-type titaniumdioxide sol by heat treating hydrated titanium oxide and alkali metalhydroxide and maturing in hydrochloric acid aqueous solution.

SUMMARY OF THE INVENTION

The following summarizes this invention:

Process for purifying TiO₂ ore consisting essentially of subjecting theore to two or more leaching treatments, said leaching treatments:

(a) alternating between use of an aqueous solution of a mineral acid andan aqueous solution of an alkali metal compound selected from the groupconsisting essentially of alkali metal carbonates, hydroxides ormixtures thereof,

(b) being carried out at a temperature, pressure, and time, and with anamount and concentration of an aqueous solution of a mineral acid and anaqueous solution of an alkali metal compound, which are sufficient tosolubilize substantially the iron, alkali metal, alkaline earth metal,rare earth metal, aluminum, phosphorous, thorium, uranium, chromium,manganese, silicon, vanadium, and yttrium impurities present to form aleachate, and

(c) including a treatment to remove substantially the leachate from theore prior to the next leaching treatment.

There is also provided by this invention TiO₂ which is produced from thepurified TiO₂ ore of this invention by the chloride process.

In accordance with this invention, it has been found that theaforementioned impurities in TiO₂ (and especially iron, calcium,silicon, aluminum, phosphorus, magnesium, barium, strontium and theradionuclides such as thorium and uranium) ore can readily be reduced toacceptable levels. Moreover, the process is especially useful forremoving impurities which are resistant to conventional removal means,including aluminum, silicon, phosphorus, thorium, and uranium toacceptable levels. Such purified TiO₂ ore is especially suitable formaking TiO₂ pigment by the chloride process. Finally, the process ofthis invention is highly useful and desirable because it can makepractical the utilization of low grade, inexpensive and more abundantTiO₂ ore which contains numerous impurities. The process is also simpleand requires few steps. Moreover, the process of this invention can haveconsiderably less energy requirements than many prior art processesbecause a roasting step prior to leaching generally is not necessary.

DETAILED DESCRIPTION OF THE INVENTION Ore

It is believed that any TiO₂ ore in any form can be used for the processof this invention including anatase, limenite and rutile. Preferred isanatase and especially preferred is anatase from a carbonatite source.

The following sets forth the mineral composition of a typical anataseore which is suitable for being processed in accordance with one processof this invention:

    ______________________________________                                        Ti Minerals                                                                   Major:   Anatase TiO.sub.2                                                    Minor:   Ilmenite FeTiO.sub.3                                                          Schorlomite Ca.sub.3 (Fe, Ti).sub.2 (Si, Ti).sub.3 O.sub.12                   Ti-pyroxenite (e.g. Ti-biotite)                                      Fe Minerals                                                                   Major:   Magnetite Fe.sub.3 O.sub.4                                                    Maghemite Y--Fe.sub.2 O.sub.3                                        Minor:   Goethite FeOOH                                                                Hematite -Fe.sub.2 O.sub.3                                                    Ilmenite FeTiO.sub.3                                                          Schorlomite Ca.sub.3 (Fe, Ti).sub.2 (Si, Ti).sub.3 O.sub.12          Al Minerals                                                                   Major:   Wavellite Al.sub.6 (PO.sub.4).sub.4 (OH).sub.6.9H.sub.2 O                     Crandallite CaAl.sub.3 (PO.sub.4).sub.2 (OH).sub.5.H.sub.2 O         Minor:   Phlogopite KMg.sub.3 (Si.sub.3 AlO.sub.10)(OH).sub.2                 Ca Minerals                                                                   Major:   Crandallite                                                                   Hydroxyapatite Ca.sub.5 (PO.sub.4).sub.3 (OH)                                 Calcite (CaCO.sub.3)                                                 Minor:   Perovskite CaTiO.sub.3                                                        Pyroxene (e.g. Diopside)                                             P and Rare Earth Minerals                                                     Major:   Rhabdophane (La, Nd, Y)(PO.sub.4).H.sub.2 O                                   Crandallite sub-group minerals such as                                        Florencite                                                                    CeAl.sub.3 (PO.sub.4).sub.2 (OH).sub.6                               Minor:   Brockite (RE, Th)(PO.sub.4).H.sub.2 O                                         Aeschynite (Ce, Ca, Fe, Th)(Ti, Nb).sub.2 (O, OH).sub.6              Other Minerals (gangue)                                                       Vermiculite Mg.sub.11 Al.sub.5 FeSi.sub.11 O.sub.42.4OH.sub.2 O               Quartz SiO.sub.2                                                              Wavellite Al.sub.6 (PO.sub.4).sub.4 (OH).sub.6.9H.sub.2 O                     Some amorphous phase                                                          Pyroxenes                                                                     Clay minerals                                                                 ______________________________________                                    

Impurities

The impurities which can be removed in accordance with the process ofthis invention include alkali metals, alkaline earth metals, rare earthmetals, iron, aluminum, phosphorous, thorium, uranium, chromium,maganese, silicon, vanadium and yttrium. Especially suitable for removalby the process of this invention are the impurities of iron, phosphorus,aluminum, calcium, barium, strontium, chromium, manganese, silicon,vanadium, yttrium, lanthanum, cerium, neodymium, thorium, and uranium.The impurities of phosphorus, silicon, aluminum, iron, calcium, barium,strontium, and radionuclides such as thorium and uranium are especiallydetrimental to the chloride process for making TiO₂ pigment; suchimpurities can be readily reduced to acceptable levels by the process ofthis invention. Also, while the impurities of aluminum, phosphorus,silicon, thorium, and uranium are especially resistant to removal byconventional chemical or mechanical means, they can readily be reducedto acceptable levels by the process of this invention. By the term"impurities" is meant the foregoing metals in their elemental state,oxides thereof, salts thereof and other complexes thereof.

Particle Size of Ore

For the process of this invention, preferably, the ore should be inparticulate form. The optimum particle size for any TiO₂ ore desired tobe processed can readily be determined by comminuting (such as bygrinding, crushing, milling, etc.) the ore into several differentparticle sizes and evaluating the amount of impurities removed by theprocess of this invention.

Generally, it can be desirable to liberate the minerals to be separatedfrom the ore, i.e., to comminute the ore into as fine particles aspractical so that the presence of discrete minerals or nearly discreteminerals in the particles is substantially improved, i.e., by at least10%.

Ordinarily, the ore should have a particle size of less than aboutone-fourth inch. If ore treated in accordance with this invention is tobe used in the chloride process for making Ti02, its particle size canbe adjusted so that it is compatible with such process. In such case,the particles preferably will fall within the range of about -20 mesh to+400 mesh. Of course, some ores in their natural state have a particlesize within this range. If so, additional comminuting is not necessary.

Mineral Dressing

If desired, the ore can be subjected to mineral dressing prior to theleaching treatments. By mineral dressing is meant mechanical processeswhich can remove some of the undesired impurities, including desliming(removing fine particles by a cyclone, grating or settling process),crushing, grinding, classification, screening, flotation, electrostaticseparation and magnetic separation. Suitable mineral dressing processesare disclosed in U.S. Pat. No. 4,243,179, which is hereby incorporatedby reference. If mineral dressing is used, it can be designed to reducethe ore to the desired particle size.

Roasting

Generally, it has been found that for most ores, a roasting prior to theleaching treatments of this invention is not necessary, and if too higha temperature is used, it can be detrimental to the leaching treatments.Consequently, if roasting is used, then preferably a temperature of lessthan about 700° C., and more preferably less than about 400° C. and mostpreferably less than 300° C. should be used.

If roasting is used, it can be carried out by any suitable means,process or device. For example, a fixed bed, rotary kiln, fluidized bed,batch or continuous process can be utilized.

Leaching

For the leaching steps, there are utilized two or more leachingtreatments, which alternate between use of aqueous solution of a mineralacid and an aqueous solution of an alkali metal compound selected fromthe group consisting essentially of alkali metal carbonates, hydroxidesor mixtures thereof.

Preferred acids are ferric chloride, hydrochloric acid, nitric acid,sulfuric acid, hydrofluoric acid, and mixtures thereof. Especiallypreferred are hydrochloric acid, nitric acid, hydrofluoric acid, andmixtures thereof. Most especially preferred is hydrochloric acid.

The acid should be utilized in an effective amount, i.e., an amount andconcentration sufficient to solubilize substantially the impurities.Analysis of the leachate, i.e., the acid solution containing thedissolved impurities, and the leached ore can readily determine whetheror not the amount and/or concentration of acid is sufficient. The acidconcentration should be at least 1% by weight, based on the total weightof the solution. Ordinarily, the acid will be present in an amount ofabout 1-40% by weight, based on the total weight of the solution.Preferably, the concentration of the acid will be about 3-35 percent,more preferably about 5-25 percent, and most preferably about 10-20percent by weight based on the total weight of the solution.

The acid leaching treatment will take place at a temperature andpressure, and for a time which is sufficient to solubilize substantiallythe mineral impurities present. Ordinarily, the time required will be atleast about 10 minutes. Typical ranges of time are about 10 minutes toeight hours, preferably about 15 minutes to four hours and mostpreferably about 20-40 minutes. The temperature will ordinarily be atleast about ambient temperature. Typical temperature ranges are aboutambient to 150° C., and most preferably about ambient to 120° C.Ordinarily, the pressure range will about 1-10 atmospheres absolute,preferably about 1-5 atmospheres absolute, and most preferably about 1-2atmospheres absolute.

Suitable alkali metal compounds which can be used in the leachingtreatment include sodium hydroxide, sodium carbonate, potassiumhydroxide, potassium carbonate, lithium hydroxide, and lithiumcarbonate. Preferred are sodium hydroxide and sodium carbonate. Mostpreferred is sodium hydroxide.

The alkali metal compound should be used in an effective amount, i.e.,an amount and concentration sufficient to solubilize substantially theimpurities. Analysis of the leachate, i.e., the solution of the alkalimetal compound containing the dissolved impurities, and the leached orecan readily determine whether or not the amount and concentration ofalkali metal compound are sufficient. Ordinarily, the concentration ofalkali metal compound will be about 2-50 percent, preferably about 10-40percent, and most preferably about 20 to 30 percent by weight, based onthe total weight of the solution.

The leaching treatment with the aqueous solution of an alkali metalcompound will take place at a temperature, pressure, and time which issufficient to solubilize substantially the mineral impurities present.Ordinarily, the time required will be at least about 10 minutes. Typicalranges of time are about 10 minutes to eight hours, preferably about 15minutes to four hours, and most preferably about 20-40 minutes. Thetemperature ordinarily will be about 60°-240° C., preferably about130°-210° C., and most preferably about 180°-210° C. The pressuregenerally will be about 1-30 atmospheres, preferably about 3-18atmospheres, and most preferably about 9-18 atmospheres absolute.

In regard to the number of leaching treatments, generally they will notexceed about 10, preferably they will not exceed about 5 and mostpreferably, they will not exceed about 3. Often, two or three leachingsteps will be adequate. Ordinarily, to reduce processing costs, it isdesirable to use the fewest steps which will still remove the desiredamount of impurities.

By the term "solubilize substantially," as used to describe the leachingtreatment, is meant the concentration of acid and alkali metal compoundand conditions of temperature, pressure, and time which will solubilizeat least about 10% by weight of the total impurities. Preferably, atleast 50% of the total impurities will be solubilized. Often, a graph ofthe concentration of the acid or alkali metal compound and conditions oftemperature and time, compared to the amount of impurities removed willhelp to determine trends and optimizations.

Removing the Leachate

Following each leaching step, the leachate is removed from the treatedTiO₂ ore. Preferably, this is done by removing the leachate followed bywashing with water or by washing with water alone. Preferably, the waterwill be hot, i.e., up to its boiling point. The amount of washingrequired can readily be determined by analyzing the wash water for thepresence of impurities and acid or alkali metal carbonates ofhydroxides.

Use of Treated Ore

After the ore has been treated in accordance

with the process of this invention, it can be used to make TiO₂ pigmentor titanium metal or be used in any process where a purified TiO₂ ore isdesired. Preferably, the TiO₂ ore treated by the process of thisinvention can be used to make TiO₂ pigment, and most preferably, to makeTiO₂ pigment by the chloride process. Suitable chloride proceses andreactors for using the TiO₂ ore treated in accordance with the processof this invention are disclosed in U.S. Pat. Nos. 2,488,439, 2,488,440,2,559,638, 3,203,763, 2,833,626, 3,284,159, and 2,653,078, which arehereby incorporated by reference.

The following examples illustrate this invention. Unless otherwiseindicated, all percentages are percent by weight.

EXAMPLE I

A flotation concentrate of a titanium ore containing 74.45% TiO₂, withthe composition shown in Table I, column (a), and with a particle sizefiner than 200 mesh, was leached with nine times its weight of 20% HClby stirring for two hours at 90° C. The hot suspension was then filteredand the solids washed with hot water ,and dried. The dried solid wasthen leached with 10% NaOH by shaking in a pressure container at aboutone cycle/two seconds for one hour at 180° C. and 8-10 atmospheres. Thepressure container was then vented and opened and the contents filteredhot (ca. 100° C.). The solids were washed with hot H₂ O and dried.Analysis of the product is shown in Table I, column (b).

EXAMPLE II

A flotation concentrate of a titanium ore containing 74.45% TiO₂, withthe composition shown in Table I, column (a), and with a particle sizefiner than 200 mesh, was leached with 25% NaOH by shaking in a pressurecontainer at about one cycle/two seconds for one hour at 210° C. and 18atmospheres. The pressure container was then vented and opened and thecontents filtered hot. The solids were washed with hot H₂ O and dried.The dried solid was then leached with nine times its weight of 20% HClby stirring for four hours at 90° C. The hot suspension was thenfiltered, and the solids washed with hot water and dried. Analysis ofthe product is shown in Table I, column (c).

                  TABLE I                                                         ______________________________________                                                (a)         (b)     (c)                                                       Starting.   HCl/    NaOH/                                                     Material    NaOH    HCl                                               ______________________________________                                        TiO.sub.2 (%)                                                                           74.45         90.26   94.95                                         FE.sub.2 O.sub.3 (%)                                                                    4.74          4.95    1.61                                          Al.sub.2 O.sub.3 (%)                                                                    2.97          0.10    0.00                                          CaO (%)   3.60          0.42    0.20                                          BaO (%)   0.28          0.17    0.05                                          SrO (%)   0.21          0.10    0.00                                          Cr.sub.2 O.sub.3 (%)                                                                    0.00          0.00    0.00                                          MgO (%)   0.00          0.00    0.00                                          Nb.sub.2 O.sub.5 (%)                                                                    0.82          1.01    1.16                                          P.sub.2 O.sub.5 (%)                                                                     4.35          0.15    0.80                                          SiO.sub.2 (%)                                                                           1.03          0.83    0.49                                          V.sub.2 O.sub.5 (%)                                                                     0.13          0.10    0.06                                          ZrO.sub.2 (%)                                                                           0.37          0.41    0.37                                          Y.sub.2 O.sub.3 (%)                                                                     0.03          0.01    0.00                                          La.sub.2 O.sub.3 (%)                                                                    0.47          0.31    0.06                                          CeO.sub.2 (%)                                                                           0.94          0.64    0.08                                          Nd.sub.2 O.sub.3 (%)                                                                    0.35          0.23    0.08                                          Th (ppm)  300           170     35                                            U (ppm)   150           120     20                                            ______________________________________                                    

EXAMPLE III

The starting ore had a typical particle size in minus 10 mesh to plus170 mesh range, with greater than 70% of the ore particles coarser than70 mesh. The composition of the starting ore is shown in Table II,column (d).

Forty grams of the starting ore were mixed with 400 milliliters of 20%HCl solution. The slurry was then heated to 90 degrees centigrade underconstant agitation of 200 rpm. The leaching was carried out under refluxfor 120 minutes. The slurry was then filtered in a Buchner funnel,washed three times with 200 milliliters of hot water, and dried.

Twenty-eight grams of the above HCl-leached ore were then leached againin a caustic solution under the following conditions:

    ______________________________________                                        NaOH              280 milliliters (30%)                                       Temperature       210 degrees centigrade                                      Pressure          approx. 13 atmospheres                                      Agitation         200 rpm                                                     Leach Time        60 minutes                                                  ______________________________________                                    

After the hydrothermal caustic leaching, the ore was filtered in aBuchner funnel and washed with 200 milliliters hot water at least 3times, and dried.

Twenty-five grams of the double-leached ore were then finally leachedagain in HCl under the following conditions:

    ______________________________________                                        20% HCl         250 milliliters                                               Temperature     90 degrees centigrade                                         Agitation       200 rpm                                                       Leach time      120 minutes (under reflux)                                    ______________________________________                                    

Chemical analysis of the beneficiated ore samples as well as thestarting ore is shown in Table II.

                  TABLE II                                                        ______________________________________                                                 Leach           (d)                                                           (a)   (b)        (c)    Starting                                              HCl   NaOH       HCl    Material                                     ______________________________________                                        TiO.sub.2  83.44   81.81      91.91                                                                              65.42                                      Fe.sub.2 O.sub.3                                                                         4.84    4.32       3.81 13.80                                      Al.sub.2 O.sub.3                                                                         2.86    .31        .41  4.20                                       CAO        .25     .23        .09  2.13                                       BAO        .15     .14        .12  0.46                                       SRO        .09     .08        .01  0.32                                       CR.sub.2 O.sub.3                                                                         0       0          0    0                                          MgO        0       0          .10  0                                          MnO        .22     .21        .18  0.61                                       Nb.sub.2 O.sub.5                                                                         1.03    1.02       1.23 0.76                                       P.sub.2 O.sub.5                                                                          3.28    .63        .80  5.89                                       SiO.sub.2  2.99    .61        .67  1.69                                       V.sub.2 O.sub.5                                                                          .12     .06        .11  0.11                                       ZRO.sub.2  .47     .38        .35  0.44                                       Y.sub.2 O.sub.3                                                                          .02     .01        0    0.05                                       La.sub.2 O.sub.3                                                                         .21     .20        .09  0.61                                       CeO.sub.2  .50     .48        .21  1.18                                       NdO.sub.3  .12     .11        .01  0.47                                       TH (ppm)   168     168        92   325                                        U (ppm)    96      91         55   120                                        ______________________________________                                    

The invention claimed is:
 1. Process for purifying TiO₂ ore containingimpurities of iron, alkali metal, alkaline earth metal, rare earthmetal, aluminum, phosphorus, thorium, uranium, chromium, manganese,silicon, vanadium, and yttrium, said process consisting essentially ofsubjecting the ore to two or more leaching treatments, said leachingtreatment:(a) alternating between use of an aqueous solution of amineral acid and an aqueous solution of an alkali metal compoundselected from the group consisting essentially of alkali metalcarbonates, hydroxides or mixtures thereof, and wherein the treatmentwith a mineral acid occurs first, and (b) being conducted at atemperature, pressure, and time, and with an amount and concentration ofan aqueous solution of a mineral acid and an aqueous solution of analkali metal compound, which are sufficient to solubilize substantiallythe iron, alkali metal, alkaline earth metal, rare earth metal,aluminum, phosphorus, thorium, uranium, chromium, manganese, silicon,vanadium, and yttrium impurities present to form a leachate, and whereinthe leachate formed is removed prior to the next leaching treatment. 2.The process of claim 1 wherein the alkali metal compound used for theleaching treatment consists essentially of sodium hydroxide, sodiumcarbonate or mixtures thereof, and the mineral acid used for theleaching treatment consists essentially of hydrochloric acid, sulfuricacid, nitric acid, hydrofluoric acid or mixtures thereof.
 3. The processof claim 2 wherein the alkali metal compound used for the leachingtreatment is present in an amount of about 2-50% by weight, based on thetotal weight of the solution; the mineral acid used for the leachingtreatment is present in an amount of about 1-40% by weight, based on thetotal weight of the solution; and the TiO₂ ore has a particle size ofabout -20 to +400 mesh.
 4. The process of claim 3 wherein the alkalimetal compound used for the leaching treatment is present in an amountof about 10-40% by weight, based on the total weight of the solution,and the mineral acid used for the leaching treatment is present in anamount of about 3-35% by weight, based on the total weight of thesolution.
 5. The process of claim 3 wherein the alkali metal compoundused for the leaching treatment is present in an amount of about 20-30%by weight, based on the total weight of the solution, and the mineralacid used for the leaching treatment is present in an amount of about5-25% by weight, based on the total weight of the solution.
 6. Theprocess of claim 3 wherein the alkali metal compound is sodium hydroxidewhich is present in an amount of about 10-40% by weight, and the acid ishydrochloric acid which is present in an amount of about 3-35% byweight.
 7. The process of claim 1 wherein prior to the leachingtreatments the ore is subjected to mineral dressing; the leachingtreatment with an aqueous solution of a mineral acid takes place at atemperature of about ambient to about 150° C., a pressure of about 1-10atmospheres, and for a time of about 10 minutes to about 8 hours; theleaching treatment with a solution of an alkali metal compound takesplace at a temperature of about 60-240° C., a pressure of about 1-30atmospheres, and a time of about 10 minutes to about 8 hours; and theremoval of the leachate includes washing with water.
 8. The process ofclaim 2 wherein prior to the leaching treatments the ore is subjected tomineral dressing; the leaching treatment with an aqueous solution of amineral acid takes place at a temperature of about ambient to about 150°C., a pressure of about 1-10 atmospheres, and for a time of about 10minutes to about 8 hours; the leaching treatment with an aqueoussolution of an alkali metal compound takes place at a temperature ofabout 60°-240° C., a pressure of about 1-30 atmospheres, and a time ofabout 10 minutes to about 8 hours; and the removal of the leachateincludes washing with water.
 9. The process of claim 3 wherein prior tothe leaching treatments the ore is subjected to mineral dressing; theleaching treatment with an aqueous solution of a mineral acid takesplace at a temperature of about ambient to about 150° C., a pressure ofabout 1-10 atmospheres, and for a time of about 10 minutes to about 8hours; the leaching treatment with an aqueous solution of an alkalimetal compound takes place at a temperature of about 60-240° C., apressure of about 1-30 atmospheres, and a time of about 10 minutes toabout 8 hours; and the removal of the leachate includes washing withwater.
 10. The process of claim 4 wherein prior to the leachingtreatments the ore is subjected to mineral dressing; the leachingtreatment with an aqueous solution of a mineral acid takes place at atemperature of about ambient to about 150° C., a pressure of about 1-10atmospheres, and for a time of about 10 minutes to about 8 hours; theleaching treatment with an aqueous solution of an alkali metal compoundtakes place at a temperature of about 60°-240° C., a pressure of about1-30 atmospheres, and a time of about 10 minutes to about 8 hours; andthe removal of the leachate includes washing with water.
 11. The processof claim 5 wherein prior to the leaching treatments the ore is subjectedto mineral dressing; the leaching treatment with an aqueous solution ofa mineral acid takes place at a temperature of about ambient to about150° C., and a pressure of about 1-10 atmospheres, and for a time ofabout 10 minutes to about 8 hours; the leaching treatment with anaqueous solution of an alkali metal compound takes place at atemperature of about 60°-240° C., a pressure of about 1-30 atmospheres,and a time of about 10 minutes to about 8 hours; and the removal of theleachate includes washing with water.
 12. The process of claim 6 whereinthe ore is anatase; prior to the leaching treatments the ore issubjected to mineral dressing; the leaching treatment with an aqueoussolution of a mineral acid takes place at a temperature of about ambientto about 150° C., a pressure of about 1-10 atmospheres, and for a timeof about 10 minutes to about 8 hours; the leaching treatment with anaqueous solution of an alkali metal compound takes place at atemperature of about 60-240° C., a pressure of about 1-30 atmospheres,and a time of about 10 minutes to about 8 hours; and the removal of theleachate includes washing with water.
 13. The process of claim 7 whereinthe leaching treatment with an aqueous solution of an alkali metalcompound takes place at a temperature of about 30°-210° C. and apressure of about 3-18 atmospheres.
 14. The process of claim 8 whereinthe leaching treatment with an aqueous solution of an alkali metalcompound takes place at a temperature of about 130°-210° C. and apressure of about 3-18 atmospheres.
 15. The process of claim 9 whereinthe leaching treatment with an aqueous solution of an alkali metalcompound takes place at a temperature of about 130°-210° C. and apressure of about 3-18 atmospheres.
 16. The process of claim 10 whereinthe leaching treatment with an aqueous solution of an alkali metalcompound takes place at a temperature of about 130°-210° C. and apressure of about 3-18 atmospheres.
 17. The process of claim 11 whereinthe leaching treatment with an aqueous solution of an alkali metalcompound takes place at a temperature of about 130°-210° C. and apressure of about 3-18 atmospheres.
 18. The process of claim 12 whereinthe leaching treatment with an aqueous solution of an alkali metalcompound takes place at a temperature of about 130°-210° C. and apressure of about 3-18 atmospheres.
 19. The process of any of claims1-18 wherein the first leaching treatment uses an aqueous solution of amineral acid, and the total number of leaching treatments does notexceed about
 10. 20. The process of any of claims 1-18 wherein the firstleaching treatment uses an aqueous solution of a mineral acid, and thetotal number of leaching treatments does not exceed about
 5. 21. Theprocess of any claim 1-18 wherein the first leaching treatment uses anaqueous solution of a mineral acid, and the total number of leachingtreatment does not exceed about
 3. 22. The process of any of claim 1-18wherein the first leaching treatment uses an aqueous solution of amineral acid, and the total number of leaching treatment does not exceed2.
 23. The process of any of claim 1-18 wherein either (a) there is noroasting prior to leaching or (b) if roasting is done prior to leaching,it is carried out at a temperature of less than about 700° C.
 24. Theprocess of any of claims 1-18 wherein either (a) there is no roastingprior to leaching or (b) if roasting is done prior to leaching, it iscarried out at a temperature of less than about 700° C., and the totalnumber of leaching steps is about 2-10.
 25. The process of any of claims1-18 wherein either (a) there is no roasting prior to leaching or (b) ifroasting is done prior to leaching, it is carried out at a temperatureof less than about 700° C., and the total number of leaching steps doesnot exceed about
 3. 26. The process of any of claims 1-18 wherein either(a) there is no roasting prior to leaching or (b) if roasting is doneprior to leaching, it is carried out at a temperature of less than about700° C., the total number of leaching steps does not exceed about 3, andthe TiO₂ ore is anatase.